Now the system can parse paths to files/directories.

It follows the same Unix standard namespace.

For now, only absolute paths are allowed.

The parse mechanism relies on the struct path_part. Which represents
each component on a single path.

All the components are chain-linked through path_part->next, where the
last path component will have ->next == NULL.

This also introduces path_root struct, which represents the root of
the path.

The first component, linked to path_root->head, is always the "/" component.

The disk_id represents the disk the root directory is found into. This
should actually (and likely will) be a mountpoint not a disk id.

Signed-off-by: Carlos Maiolino <cem@toxiclabs.cc>